Objectives: 1. To document, through the use of electrophysiological recordings, the extent and type of sleep deprivation during and after the intensive care unit experience: a. The extent refers to the total amount of night-time sleep. b. the type refers to how much of each stage of sleep is recorded, i.e. is the deprivation related to only REM or slow-wave sleep. 2. To assess, to the maximal extent possible, the amount and duration of REM rebound. 3. Through pre-operative and daily post-operative neurological examinations, attempt to assess the degree to which the post-operative sleep disturbances may be related to CNS damage which occurred during surgery. 4. To assess, by extrapolation if necessary, the extent to which the sleep deprivation and CNS damage may be contributing to the development of the syndrome of post-operative psychosis. 5. This will be accomplished via pre-and post-operative nighttime recordings to include electroencephalogram (EEG), electrooculogram (EOG), electromyogram (EMG) and electrocardiogram (ECG). 6. Patients will be recorded for two nights pre-operatively, and as many nights as possible during their stay in the intensive care unit, and subsequently, during their ward convalescence.